<html>
<head>
<style>
.serif{font-family:"Times New Roman",Times,serif;}
.sansserif{font-family:Arial,Helvetica,sans-serif;}
</style>
</head>

<body>
<div class="serif">This is a div</div>
<div class="sansserif">This is a div</div>
</body>
</html>